1. Field of the Invention
The present invention concerns a computed tomography (CT) system, in particular a computed tomography system with an adjustable focal spot-to-detector distance.
2. Description of the Prior Art
In a conventional CT system, the aperture angle of the x-ray fan beam radiated by the x-ray tube and the distance between the focal spot of the x-ray tube and its corresponding detector are fixed. Not only does the accessibility to the patient during the scan process thereby decrease, but this can also lead to an impairment of the imaging quality of the system due to differences between volumes of patients (body parts) to be scanned, or differences in the quantities of the emitted/received x-rays.
In a typical CT system, a patient opening is mounted at a gantry in which a patient can be moved for scanning in the gantry. The x-ray tube is mounted on one side of the gantry and the focal spot of the x-ray tube exhibits a fixed aperture angle a of the emitted x-ray fan. A detector associated with the x-ray tube is provided on the detector mounting fastened on the other side of the gantry in order to receive x-ray radiation emitted by the focal spot for a system imaging.
Since the aperture angle of the x-ray fan emitted by the focal spot of the x-ray tube and the distance between the focal spot and the detector are fixed, the scanning of the patient within the patient opening is very uncomfortable when the volume of a patient to be scanned is extremely large, and the x-rays possibly do not entirely cover the volume of the patient in the FOV—field of view. If an x-ray tube with a larger aperture angle of the fan beam is used in order to overcome the such problems above, the cost of the apparatus rises significantly. If the diameter of the patient opening is increased in order to obtain a better accessibility to a patient to be scanned but the volume of the patient to be scanned is comparably small (for example a child), the amount of the x-rays passing through the patient and acquired by the detector significantly decreases, which seriously influences the quality of the imaging, although the impairment of the image quality can be partially compensated by subsequent image enhancement algorithms.
Designing a computed tomography system with an adjustable focal spot-to-detector distance is therefore a problem needing a solution in this field.